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The heat's still on

5 June 1999

TO many people’s surprise, it now seems likely that for the past century, the
Sun has been gradually pumping out more and more energy. This might seem just
what the industry lobby has been waiting for—there may be another culprit
for global warming than all those gas-guzzling cars and power plants.

But thankfully, the clever series of scientific observations linking
variations in the Sun’s and the Earth’s magnetic fields to long-term changes in the Sun’s energy output(see p 5) don’t signal a new declaration of war. Rather,
they help provide a more sensible compromise. Mainstream science, which has
supported the idea that rising temperatures are a signal of global warming
caused by human activity, and the sceptics who have pointed to a variety of
other possible causes, including cycles in the Sun’s behaviour, now look as
though they have both been right.

Changes in the Sun’s energy output can account for much of the slow warm-up
early this century. But the faster warming since the early 1970s seems to have
been caused mainly by greenhouses gases.

While both camps might claim to have been right about the causes of global
warming, only one group can be right about what to do next. If human activity is
mainly responsible for changing temperatures now, it is back to persuading
governments to change their policies immediately.